Field of the Invention
The present invention relates to the field of daytime or night-time visual observation appliances and, more particularly, an optoelectronic surveillance system in the visible or infrared range.
Brief Discussion of the Related Art
Such an optoelectronic surveillance system is in particular used for monitoring the space surrounding a vehicle, in particular a land or sea vehicle, in order to detect the appearance of an obstacle, another vehicle or a projectile in the zone being monitored. To this end, the optoelectronic surveillance system is arranged to provide images of the space being monitored to an operator and to process the images with a view to issuing an alert automatically in the event of intrusion into the space being monitored.
An optoelectronic surveillance system generally comprises an acquisition unit comprising at least one sensor mounted behind a zoom having a substantially horizontal line of sight. The acquisition unit is mounted so as to turn about a substantially vertical axis and is connected to a control unit arranged so as to control the acquisition unit so as to capture images on the fly during the rotation of the acquisition unit about the vertical axis. The images will then be assembled in order to form panoramic images of the environment. This makes it possible to sweep the horizon over 360° around the acquisition unit.
It appears that these systems are more effective, the higher the rotation speed of the acquisition unit. However, the rotation speed is limited because of the integration time of the sensor, which is the time necessary for acquiring the image signal coming from a scene and is equivalent to the exposure time in photography. As a result, if the rotation speed is too high, the images are affected by movement fuzziness. This is all the more true with the infrared acquisition units used in cold geographical regions.
To remedy this drawback, disposing, in front of the zoom, a reflective optical element that is mounted so as to rotate about an axis parallel to the rotation axis of the acquisition member is known. The reflective optical element is in the form of a polygon, the faces of which parallel to the rotation axis are reflective and which is rotated in a direction opposite to the rotation direction of the acquisition unit, at a speed equal to half the rotation speed of the acquisition unit. Thus the opposite rotations of the reflective optical element and of the acquisition unit make it possible to keep the line of sight substantially fixed in the space of the scene observed for a time greater than the integration time of the sensor. These devices are heavy and bulky.